The aerodynamic performance, hence efficiency, of airfoils, rotor blades, wings, turbine/compressor blades, and windmill blades, is strongly dependent upon the lift-to-drag (L/D) ratio of such airfoils. To this end, active flow control (AFC) techniques have been utilized to increase the L/D ratio. These AFC techniques include providing ports and/or openings through the surface of such airfoils and applying steady blowing, steady suction, or alternating blowing and suction of fluid therefrom. Such AFC techniques have proven to be effective in increasing the lift coefficient of airfoils, decreasing their drag coefficient, or both in a manner that increases the overall L/D ratio of the airfoils, and thereby increasing their aerodynamic efficiency.
AFC techniques are particularly advantageous in situations where large flow separations over such airfoils would otherwise exist. Such situations frequently occur when airfoils are orientated at high angles-of-attack and when flaps are utilized to generate relatively high lift. As is the case with virtually all types of aerodynamic control surfaces, a drag penalty is usually incurred when fluid flow over the top surface (or the lower pressure surface) of the airfoil separates upstream of the trailing edge of the airfoil. The size of the separated flow region forward of the trailing edge depends on, among other things, the free stream angle-of-attack, the flow speed, the airfoil cord length, and, for flapped airfoils, the flap chord length and the flap deflection angle. Additionally, such separation is accompanied by a detrimental recirculation flow region downstream of the separation point. By reducing or delaying flow separation, a corresponding increase in lift and/or reduction in drag can be achieved.